JP6733772B1 - Press molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a press-molding method for press-molding a press-molded product having a hat-shaped cross section which is convexly curved in the height direction while suppressing cracks and wrinkles. A press molding method according to the present invention has a hat-shaped cross-section having a top plate portion 3, a vertical wall portion 5, and a flange portion 7, and has a convex shape in a height direction along a longitudinal direction in a side view. A press-formed product 1 having a curved convex curved portion 11 is formed, which includes a top plate equivalent portion 23, and a vertical wall equivalent portion 25 including a twisted vertical wall portion 25a twisted along the longitudinal direction. And a second molding step of press-molding the intermediate molded product 21 having a portion corresponding to the convex curve 31 to press-mold the intermediate molded product 21 into the press-molded product 1 having a target shape. The twisted vertical wall portion 25a in the first molding step is twisted such that the angle formed with the top plate equivalent portion 23 is larger on the end side than the center of the convex curved equivalent portion 31 in the longitudinal direction. It is a feature. [Selection diagram]

Description

The present invention relates to a press-molding method, and particularly to a press-molded product having a top plate portion, a vertical wall portion, and a flange portion, which has a cross-sectional hat shape, and which is convexly curved in the height direction along the longitudinal direction in a side view. The present invention relates to a press molding method.

Press molding is a method in which a metal material such as a steel plate is sandwiched between molds to transfer the shape of the molds for processing. In particular, many automobile parts are manufactured by press molding. Recently, from the viewpoint of reducing the weight of automobile bodies, there is an increasing tendency to use high-strength steel sheets (high-tensile steel sheets) for vehicle body parts. However, ductility tends to become poor as strength increases as a characteristic of steel plates and other metal materials, so that press forming of high-strength steel plates often causes molding defects such as cracks and wrinkles, which is a problem.

Among skeletal parts of an automobile body, curved parts having a sharply curved shape such as a front side member and a rear side member are difficult to form because cracks and wrinkles easily occur when manufactured by press molding. Recently, automobile companies and parts companies are considering applying high-strength steel sheets to the manufacture of curved parts for the purpose of further reducing the weight of automobile bodies, and how to perform press forming while preventing cracks and wrinkles. Is an issue.

Up to now, there have been proposed some techniques for press-forming curved parts while suppressing cracks and wrinkles.
For example, in Patent Document 1, in press-molding an L-shaped part curved in a top view, a punching force of a flange and a vertical wall is used to slide the material on the punch bottom surface of the material to form a wrinkle on the punch bottom. And the technique of avoiding the crack of the flange is disclosed.

Patent Document 2 proposes a method for preventing out-of-plane deformation and suppressing wrinkles by performing draw forming while pressing the blank punch bottom with a pad in the plate thickness direction for a component curved in the vertical direction. Has been done.

In Patent Document 3, in a press forming of a curved press part having a hat-shaped cross section that is curved in the longitudinal direction, a bending portion is provided to the width direction end portion of the blank material by preforming, and the bending portion is left. A technique for suppressing the generation of wrinkles in the flange portion by press-molding the curved press component is disclosed. According to the technique, the bending at the widthwise end of the blank material in the preforming increases the rigidity of the widthwise end, and the resistance against the contracting force in the longitudinal direction becomes large. It is said that it is possible to suppress the occurrence of wrinkles in the flange portion even if the force of shrinking in the longitudinal direction due to the excess due to the shape acts.

Further, some techniques have been proposed for press-molding curved parts with beads for the purpose of suppressing the occurrence of cracks and wrinkles.
In Patent Document 4, when the end portion of the material has a curvature when viewed in a plan view and has a flange surface below the vertical wall surface when viewed in a side view, it is convex on the vertical wall surface in one step. There is disclosed a technique in which a wrinkle in a material forming portion is suppressed by providing a bead and a concave bead on a flange surface immediately below.

Japanese Patent No. 5146829 Japanese Patent No. 5733475 Patent No. 5965159 JP, 2010-115674, A

However, the technique disclosed in Patent Document 1 can be applied because the material cannot be largely moved when the punch bottom has a shape such as a seating surface or when the punch bottom has a closed shape such as a bag shape. The number of parts was limited.

In the technique disclosed in Patent Document 2, a blank holder and a pad are used at the same time for molding, and when the blank holder or the pad remains pressed when the molded product is removed from the mold, the molded product is Since it will be crushed, a locking mechanism that stops the movement is required. However, since a press device equipped with this mechanism is not general, it lacks versatility.

In the technique disclosed in Patent Document 3, the bent shape of the flange portion needs to be formed flat in the next step, but there is a risk that the bending tendency remains. In particular, in the case of automobile parts, the flange often forms a joint surface with other parts, and high surface accuracy is required. Therefore, it is necessary to pay attention to the application of this molding method.

The technique disclosed in Patent Document 4 is press working in one step, and there is a problem that the bead applied to prevent wrinkles and cracks remains as it is.

The present invention and what has been made in order to solve the above problems, a cross-sectional hat shape having a top plate portion, a vertical wall portion and a flange portion, in a convex shape in the height direction along the longitudinal direction. An object of the present invention is to provide a press-molding method capable of press-molding a curved press-molded product into a favorable shape while suppressing cracks and wrinkles.

(1) The press molding method according to the present invention has a hat-shaped cross section having a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion. Part and/or the flange part is for molding a press-formed product having a convex curved portion that is convexly curved in the height direction along the longitudinal direction in a side view, and corresponds to the top plate part. A plate-corresponding portion and a vertical wall-corresponding portion that corresponds to the vertical wall portion and includes a twisted vertical wall portion that is twisted along the longitudinal direction, and is equivalent to a convex curved portion that corresponds to the convex curved portion. A first molding step of press-molding an intermediate molded product having parts, and a second molding step of press-molding the intermediate molded product into the press-molded product, wherein the twisted vertical wall portion in the first molding process is It is characterized in that the angle formed with the portion corresponding to the top plate is twisted so that the end side is larger than the center in the longitudinal direction of the portion corresponding to the convex curve.

(2) In the structure described in (1) above, the twist vertical wall portion in the first forming step is set such that the twist amount T given by the following equation is in the range of 10° to 20°. It is characterized by that.
T=Δθ×(H/L)
However,
Δθ: Angle difference (=θ ₂ −θ ₁ )
θ ₁ : Angle (°) between the vertical wall of the twist and the equivalent part of the top plate at the center in the longitudinal direction of the part corresponding to the convex curve
θ ₂ : Angle (°) between the vertical wall of the twist and the top plate equivalent at the longitudinal end of the vertical wall
H: Vertical wall height of twisted vertical wall (mm)
L: Length of twisted vertical wall in the longitudinal direction (mm)

In the present invention, a top plate portion, a vertical wall portion continuous from the top plate portion, and a cross-sectional hat shape having a flange portion continuous from the vertical wall portion, the top plate portion and / or the flange portion Is for forming a press-formed product having a convex curved portion that is convexly curved in the height direction along the longitudinal direction in a side view, wherein a top plate equivalent portion corresponding to the top plate portion and the vertical And a vertical wall corresponding portion including a twisted vertical wall portion having a shape twisted along the longitudinal direction, which corresponds to the wall portion, and an intermediate molded product having a convex curved portion corresponding to the convex curved portion. A first molding step of press-molding and a second molding step of press-molding the intermediate molded article into a press-molded article having a target shape, and the twisted vertical wall portion in the first molding step corresponds to the top plate. Since the angle formed with the portion is twisted so that the end side is larger than the center in the longitudinal direction of the portion corresponding to the convex curve, it is possible to cause shear deformation in the twisted vertical wall portion, resulting in cracks and wrinkles. It is possible to press-form the press-formed product into a good shape by suppressing the occurrence of

It is a figure explaining the intermediate molded product press-molded in the press molding method which concerns on embodiment of this invention, and the press-molded product which is a target shape ((a-1) Perspective view of an intermediate molded product, (a-2). ) A view showing the cross section of the center of the convex curved portion and the cross section of the end portion in the longitudinal direction in the intermediate molded product, (b) a perspective view of the press molded product). It is a figure explaining the press-molded article used as a shaping|molding object in this invention ((a) perspective view, (b) top view, (c) side view). FIG. 2 is a cross-sectional view perpendicular to the longitudinal direction of a press-formed product which is a molding target in the present invention. It is a figure explaining movement of a material at the time of press-molding the press-molding object made into the object of molding by the present invention by the conventional press-molding method, and a portion in which tensile deformation and compression deformation occur in the press-molding object. It is a figure explaining movement of a material at the time of reaching the present invention, when shear deformation is generated and a vertical wall part is press-formed. It is a figure explaining the intermediate molded product press-molded by the 1st molding process of the press molding method which concerns on embodiment of this invention ((a) perspective view, (b) top view, (c) side view). It is a figure which shows the in-plane shear deformation in the twist vertical wall part of the intermediate molded product press-molded by the press-molding method which concerns on embodiment of this invention. It is a figure which shows the vertical wall height and the longitudinal direction length which give the amount of twist of the twist vertical wall part of the intermediate|middle molded product press-formed by the press-forming method which concerns on embodiment of this invention. It is a figure which shows the case where the vertical wall height of the twist vertical wall part of the intermediate molded product press-molded by the press-molding method which concerns on embodiment of this invention is changed ((a) perspective view, (b) top view. , (C) side view). It is a figure which shows the case where the longitudinal direction length of the twist vertical wall part of the intermediate molded product press-molded by the press-molding method which concerns on embodiment of this invention is changed ((a) perspective view, (b) top view. , (C) side view). It is a figure which shows the intermediate|middle molded product which has the twisted vertical wall part of the curved surface shape twisted in the opposite direction from the twisted vertical wall part of the intermediate molded product press-molded by the press molding method which concerns on embodiment of this invention ((a ) Perspective view, (b) top view, (c) side view). It is a figure which shows the in-plane shear deformation in the twisted vertical wall part twisted in the direction opposite to the twisted vertical wall part of the intermediate molded product press-formed by the press-forming method according to the embodiment of the present invention. It is a figure which shows the other example of the intermediate molded product press-molded by the press-molding method which concerns on embodiment of this invention ((a) perspective view, (b) top view, (c) side view). It is a figure which shows the other example of the press-molded article used as a shaping|molding object in this invention ((a) Only a top plate part curves convexly, (b) Only a flange part curves convexly). It is a figure explaining the draw molding and foam molding which are applied with the press molding method which concerns on embodiment of this invention ((a), (b) draw molding, (c), (d) foam molding). It is a figure explaining the cross-sectional shape orthogonal to the longitudinal direction of the press-molded article used as a shaping|molding object in a present Example. It is a figure explaining the cross-sectional shape of the twisted vertical wall part of the intermediate molded product press-molded in this Example at right angles to the longitudinal direction ((a): convex curved center, (b) longitudinal direction end part).

Prior to explaining the press-molding method according to the embodiment of the present invention, the press-molded product to be molded in the present invention, the reason why cracks and wrinkles occur when press-molding the press-molded product, and further The background to the present invention will be described. In addition, in the present embodiment, the height direction of the press-formed product is supposed to coincide with the press-formed direction of the press-formed product.

<Press-formed products>
As shown by way of example in FIGS. 2 and 3, the press-formed product 1 to be molded in the present invention has a top plate portion 3, a vertical wall portion 5 continuous from the top plate portion 3, and a vertical wall portion 5 continuous. 2 is a cross-sectional hat shape having a flange portion 7 that is formed, and the top plate portion 3 and the flange portion 7 are convexly curved in the height direction along the longitudinal direction in a side view (FIG. 2C). It has a portion 11, and linear portions 13 that extend linearly are provided on both sides in the longitudinal direction of the convex curved portion 11.
Here, the convex curved portion 11 being convexly curved in the height direction along the longitudinal direction means that the center of the convexly curved arc is located on the flange portion 7 side in a side view.

FIG. 4 shows the movement of the material during press molding when the press molded article 1 is viewed from the side. In the process of press-forming a blank (metal plate), the blank is bent at the punch shoulder R portion 4 between the top plate portion 3 and the vertical wall portion 5 and is orthogonal to the bending ridge line of the punch shoulder R portion 4. The material moves in the direction (the direction of the arrow in FIG. 4).

Therefore, in the convex curved portion 11, while the material gathers in the flange portion 7 and the length in the longitudinal direction becomes short, the length in the longitudinal direction of the top plate portion 3 becomes long, and the top plate portion 3 and the flange portion 3 become long. There is a difference in line length in the longitudinal direction with respect to 7. As a result, the top plate portion 3 is likely to be subjected to tensile deformation to cause cracking, and the flange portion 7 is likely to be subjected to compressive deformation to cause wrinkles.

From this, in order to suppress the occurrence of cracks and wrinkles when press-molding the press-formed product 1, the top plate portion 3 and the flange portion 7 in the convex curved portion 11 should not be subjected to tensile deformation or compression deformation. It is considered important to reduce the line length difference between the top plate portion 3 and the flange portion 7 in the longitudinal direction by changing the movement of the material during the press forming process.

Therefore, let us consider an ideal state in which press molding is performed without causing a line length difference in the longitudinal direction between the top plate portion 3 and the flange portion 7 in the convex curved portion 11. FIG. 5 shows the movement of the material in the ideal state. In order to prevent a line length difference between the top plate portion 3 and the flange portion 7 in the longitudinal direction from occurring, as shown in FIG. 5, a portion corresponding to the vertical wall portion 5 in the blank (hereinafter referred to as “vertical wall equivalent portion”). It is necessary to move the material in the same direction as the press forming direction by causing shear deformation in (1). However, in press molding, the mold is basically only moved in the vertical direction, and it is not easy to cause in-plane shear deformation in the material corresponding to the vertical wall by this limited mold movement.

The inventors have conducted extensive studies on a method of causing in-plane shear deformation of a material. As a result, they have found that in-plane shear deformation can be generated in the vertical wall equivalent portion by press-molding the vertical wall equivalent portion in a curved surface shape twisted out of plane along the longitudinal direction.
The present invention has been made based on such an examination, and the press molding method according to the embodiment of the present invention will be described below.

<Press molding method>
The press-molding method according to the present embodiment is for press-molding a press-molded product 1 illustrated in FIGS. 1(b) and 2 as a target shape, in which a blank is an intermediate-molded product 21 (see FIG. 1(a- 1) and (a-2)), a first molding step of preforming, and a second molding step of press molding the intermediate molded product 21 into a press molded product 1 having a target shape. The blank used in the press forming method according to the present invention may be not only a steel plate but also a thin plastic body, and examples thereof include an aluminum alloy plate, a magnesium alloy plate, a titanium alloy plate, and a resin plate. Also, the material strength of the blank is not particularly limited.

≪First molding process≫
The first molding step is a step of preforming the blank into an intermediate molded product 21 (FIGS. 1(a-1) and (a-2)).

As shown in FIG. 1(a-1), the intermediate molded product 21 corresponds to a top plate corresponding part 23 corresponding to the top plate part 3 of the press molded product 1 and a vertical wall part 5 of the press molded product 1, A cross section having a vertical wall-corresponding portion 25 including a curved vertical wall portion 25a twisted in the longitudinal direction as compared with the vertical wall portion 5, and a flange-corresponding portion 27 corresponding to the flange portion 7 of the press-formed product 1. It has a hat shape and has a convex curve corresponding portion 31 corresponding to the convex curved portion 11 of the press-formed product 1 and a straight line corresponding portion 33 corresponding to the straight line portion 13.

In the intermediate molded product 21, the twisted vertical wall portion 25 a is formed over the entire length of the vertical wall equivalent portion 25 in the longitudinal direction. In FIG. 1A-2, the center in the longitudinal direction of the portion 31 corresponding to the convex curve (hereinafter, referred to as “the center of the convex curve”) and the end portion in the longitudinal direction of the twisted vertical wall portion 25a (hereinafter, “longitudinal length”). The shape of the cross section orthogonal to the longitudinal direction of the intermediate molded product 21 at each end. The cross-sectional shape shown in FIG. 1A-2 shows the position of the flange equivalent portion 27 in the height direction for convenience of description.

As shown in FIG. 1A-2, when the angle formed by the top plate equivalent portion 23 is θ, the twisted vertical wall portion 25a is longer than the angle θ ₁ at the center of the convex curve in the longitudinal direction end portion. The angle θ ₂ at is twisted to be larger. Along with this twist, the angle θ formed by the twisted vertical wall portion 25a and the top plate equivalent portion 23 continuously changes along the longitudinal direction.

In the present embodiment, the top plate equivalent part 23 of the intermediate molded product 21 has the same shape as the top plate part 3 (FIG. 2) of the press molded product 1, as shown in FIG. On the other hand, the flange-corresponding portion 27 of the intermediate molded product 21 is continuous with the vertical wall-corresponding portion 25 including the twisted vertical wall portion 25a having a shape different from that of the vertical wall portion 5, as shown in FIG. As shown in (b) and (c), the shape is different from the flange portion 7 of the press-formed product 1 (FIGS. 2B and 2C) in plan view and side view.

Further, the angle formed by the top plate equivalent portion 23 of the intermediate molded product 21 and the twisted vertical wall portion 25a is larger at the longitudinal end portion (θ ₂ ) than at the convex curved center (θ ₁ ) (see FIG. See a-2)). Therefore, the height of the molded product in the height direction of the intermediate molded product 21 is not constant along the longitudinal direction, and is different from the height of the molded product in the height direction of the press-molded product 1.

Furthermore, the ridge line length of the punch shoulder R portion 24 (FIG. 6) between the top plate equivalent portion 23 of the intermediate molded product 21 and the vertical wall equivalent portion 25, or the vertical wall equivalent portion 25 and the flange equivalent portion 27. The ridge line length of the die shoulder R portion 26 (FIG. 6) between them is also different from the ridge line length of the punch shoulder R portion 4 and the die shoulder R portion 6 (FIG. 2) of the press-formed product 1.

For example, when the top plate equivalent portion 23 is formed in the same shape as the top plate portion 3 of the press-formed product 1 having the target shape, the ridge line length of the punch shoulder R portion 24 is the same as that of the press-formed product 1, but the die The ridge length of the shoulder R portion 26 is different from that of the press-formed product 1.
When the flange-corresponding portion 27 is formed in the same shape as the flange portion 7 of the press-formed product 1 having the target shape, even if the ridge line length of the die shoulder R portion 26 is the same as that of the press-formed product 1, the punch shoulder R portion is formed. The ridge length of 24 is different from that of the press-formed product 1.

<<Second molding step>>
The second molding step is a step of press-molding the intermediate molded product 21 (FIGS. 1(a-1) and (a-2)) into a press-molded product 1 (FIG. 1(b)) having a target shape.
By the second forming step, the vertical wall equivalent portion 25 including the twisted vertical wall portion 25a whose angle formed by the top plate equivalent portion 23 changes along the longitudinal direction is formed into the vertical wall portion 5 having the target shape. Further, the flange corresponding portion 27 is molded into the flange portion 7 having the target shape.

<<Reason to prevent cracks and wrinkles>>
Next, the reason why the press-molding method according to the present embodiment can press-mold a press-molded product that curves convexly in the height direction along the longitudinal direction in a side view while suppressing cracks and wrinkles. Will be described.

In the first molding step, as shown in FIG. 1, a vertical wall corresponding portion 25 corresponding to the vertical wall portion 5 of the press-formed product 1 has a twisted vertical wall portion 25a having a curved surface shape twisted out of plane along the longitudinal direction. To form. Thus, when the material (blank) is formed into a curved surface shape twisted out of plane, the material undergoes in-plane shear deformation in addition to out-of-plane shear deformation, as shown in FIG. 7.

As a result, the movement of the material to the center in the longitudinal direction of the flange corresponding portion 27 in the portion corresponding to the convex curve 31 is suppressed, and the movement of the material to the end side in the longitudinal direction of the top plate corresponding portion 23 is also suppressed. It Therefore, in the twisted vertical wall portion 25a, the line length difference between the line length in the longitudinal direction of the top plate corresponding portion 23 and the line length in the longitudinal direction of the flange corresponding portion 27 becomes small as shown in FIG. As a result, in the press-formed product 1 in which the intermediate-formed product 21 is press-formed into the target shape in the second forming process, cracks in the top plate portion 3 are suppressed and wrinkles in the flange portion 7 are suppressed.

≪Preferred range of twist amount of twist vertical wall≫
As shown in FIG. 7 described above, the press molding method according to the present invention causes the in-plane shear deformation of the twisted vertical wall portion 25a in the first molding step to produce the target shape of the press molded product 1 (FIG. 2). The cracks in the top plate portion 3 and the wrinkles in the flange portion 7 are suppressed.

Here, the magnitude of the in-plane shear deformation in the twisted vertical wall portion 25a depends on the degree of twist of the twisted vertical wall portion 25a. Then, in the present invention, the degree of twist of the twisted vertical wall portion 25a can be expressed by using the angle change and the aspect ratio of the twisted vertical wall portion 25a.

The angle change of the twisted vertical wall portion 25a is determined by the angle θ _{1 at} the center of the convex curve (the center in the longitudinal direction of the convex curved portion 31) of the angle formed by the twisted vertical wall portion 25a and the top plate equivalent portion 23. The angle difference Δθ from the angle θ ₂ at the directional end (the end in the longitudinal direction of the twisted vertical wall portion 25a) is given (see FIG. 1(a-2)).

As shown in FIG. 8, the aspect ratio of the twisted vertical wall portion 25a is given by a ratio H/L of the vertical wall height H and the longitudinal length L of the twisted vertical wall portion 25a. Here, the vertical wall height H and the longitudinal direction length L of the twisted vertical wall portion are the height in the direction orthogonal to the longitudinal direction and the length in the longitudinal direction in the plane of the twisted vertical wall portion 25a.

Then, the twist amount T(°) is given by the following equation (1).
T=Δθ×(H/L)=(θ ₂ −θ ₁ )×(H/L) (1)

From the formula (1), to change the twist amount T, (a) the angle θ ₁ formed by the twist vertical wall portion 25a and the top plate equivalent portion 23 at the center of the convex curve, and (b) the twist vertical direction at the end portion in the longitudinal direction. If the angle θ ₂ formed by the wall portion 25a and the top plate equivalent portion 23, (c) the vertical wall height H of the twisted vertical wall portion 25a, and (d) the longitudinal length L of the twisted vertical wall portion 25a are changed, I know it's good.

FIG. 9 shows an example of an intermediate molded product 41 in which the height H of the twisted vertical wall portion 25a is changed, and FIG. 10 is an example of an intermediate molded product 61 in which the longitudinal length L of the twisted vertical wall portion 25a is changed. Are shown respectively.

The intermediate molded product 21 shown in FIGS. 1 and 6 described above had the twisted vertical wall portion 25a formed over the entire length in the longitudinal direction. On the other hand, in the intermediate molded product 61 shown in FIG. 10, the longitudinal length L of the twisted vertical wall portion 65a is made shorter than the longitudinal length of the vertical wall portion 5 of the press molded product 1. In the intermediate molded product 61, the angle θ ₂ formed between the twisted vertical wall portion 65a and the top plate equivalent portion 63 at the end portion in the longitudinal direction is not the end portion in the longitudinal direction of the entire intermediate molded product 61, but the twisted vertical wall portion 65a. Is the angle at the longitudinal end only.

Regarding the angle between the twisted vertical wall portion 25a and the top plate equivalent portion 23 of the intermediate molded product 21 that is press-molded in the first molding step, as described above, the angle θ ₂ at the longitudinal end is equal to that at the convex curved center. It is necessary to make it larger than the angle θ ₁ . For example, when the angle θ ₂ at the longitudinal end is smaller than the angle θ _{1 at the} center of the convex curve as shown in FIG. 11, the in-plane shear deformation of the twisted vertical wall portion 25a is as shown in FIG. The direction is opposite to the twisted vertical wall portion 25a shown in FIG. Therefore, even if the intermediate molded product 81 is press-formed into the press-formed product 1 having the target shape, the line length difference in the longitudinal direction between the top plate portion 3 and the flange portion 7 cannot be reduced, and cracks and wrinkles do not occur. The suppression effect cannot be obtained.

Furthermore, the amount of twist T, which is suitable for suppressing cracks and wrinkles, was examined by simulation using the finite element method (FEM). As a result, they have found that it is desirable to suppress both cracks and wrinkles if the twist amount T is set in the range of 10° or more and 20° or less.
If the twist amount T is less than 10°, the in-plane shear deformation of the twist vertical wall portion 25a may not be sufficient. Further, when the twist amount T is more than 20°, the twist vertical wall portion 25a may be subjected to excessive shear deformation in the first forming step, and shear wrinkles may occur in the vertical wall equivalent portion.

The aspect ratio H/L of the twisted vertical wall portion 25a is the vertical wall height H at the center of the longitudinal length of the twisted vertical wall portion 25a (the intermediate position between the convex curved center and the longitudinal end portion), It may be given by using the length L in the longitudinal direction at the center in the height direction of the vertical wall.

≪Regarding the shapes of intermediate molded products and press molded products≫
In the above description, in the intermediate molded product 21 (FIGS. 1 and 6), the intermediate molded product 41 (FIG. 9), and the intermediate molded product 61 (FIG. 10), the top plate equivalent part is the top plate part having the target shape. They had the same shape, and the flange-corresponding portion had a shape different from that of the target-shaped flange portion 7.

However, in the present invention, like the intermediate molded product 101 shown in FIG. 13, the flange corresponding portion 107 has the same shape as the flange portion 7 (FIG. 2) having the target shape, and the top plate corresponding portion 103 has the target shape top plate portion. The shape may be different from the shape shown in FIG.

Also in such an intermediate molded product 101, as compared with the angle θ ₁ formed by the twist vertical wall portion 105a and the top plate equivalent portion 103 at the center of the convex curve, the twist vertical wall portion 105a and the top plate equivalent portion at the longitudinal end portion are formed. If the angle θ ₂ formed with 103 is large, the twisted vertical wall portion 105a formed in the vertical wall corresponding portion 105 undergoes in-plane shear deformation as shown in FIG. 7 and is press-formed. Therefore, in the press-formed product 1 in which the intermediate-formed product 101 is press-formed into the target shape, both cracks in the top plate portion 3 and wrinkles in the flange portion 7 can be suppressed.

However, as shown in FIG. 6, if the top plate equivalent portion 23 of the intermediate molded product 21 has the same shape as the target top plate portion 3, the intermediate molded product 21 is placed on the punch of the die used in the second molding step. Since it is possible to perform stable press molding without rattling when placed, it is possible to mold the intermediate molded product 21 of the top plate equivalent portion 23 having the same shape as the top plate portion 3 having the target shape. preferable.

Further, in the press-formed product 1 which is a molding target in the above description, both the top plate portion 3 and the flange portion 7 are curved convexly in the height direction along the longitudinal direction. As shown in FIG. 14, a press-formed product 121 in which only the top plate portion 123 is curved in a convex shape or a press-formed product 141 in which only the flange portion 147 is curved in a convex shape may be a molding target.

The above description has been made for the case where the convex curved portion 11 having a constant radius of curvature in the longitudinal direction is a molding target, as in the press-molded product 1 illustrated in FIG. However, the present invention may be applied to a press-formed product in which a plurality of convex curved portions having different radii of curvature are continuous.

In such a case, for each convex curved portion having a constant radius of curvature, the twisted vertical wall portion in the convex curved portion has a curved surface shape twisted from the center in the longitudinal direction of the convex curved portion toward the end side. Should be Then, in each convex curved portion, the top plate equivalent portion and the twisted vertical wall portion at the longitudinal end portion of the twisted vertical wall portion of the convex curved portion are formed as compared with the longitudinal center of the convex curved portion. The angle should be large.

Further, the press-formed product 1 which is a molding target in the present embodiment has the linear portions 13 on both sides in the longitudinal direction of the convex curved portion 11, but the present invention is directed to the longitudinal direction of the convex curved portion. A press-molded product having a linear portion on one side or a press-molded product having only a convex curved portion may be a molding target.

Further, in the press-formed product 1 illustrated in FIG. 2, the angle formed by the top plate portion 3 and the vertical wall portion 5 is constant along the longitudinal direction, that is, as shown in FIG. The angle θ _{1,0 at} the center of the curve (the center in the longitudinal direction of the convex curved portion 11) and the angle θ _2,0 at the longitudinal end (the longitudinal end of the vertical wall portion 5) were equal. .. However, in the present invention, the angle between the top plate portion and the vertical wall portion changes along the longitudinal direction, that is, the vertical wall portion is a press-formed product having a curved surface shape twisted along the longitudinal direction. It may be one that does.

In such a case, the angle difference between the angle at the longitudinal end of the twisted vertical wall portion of the intermediate molded product and the angle at the center in the longitudinal direction of the portion corresponding to the convex curve is calculated as the convex curve of the press molded product of the target shape. Twisting of the intermediate product by making it larger than the angle difference between the angle at the longitudinal center of the part (convex center of the convex curve) and the angle at the longitudinal end of the vertical wall (longitudinal end). The vertical wall portion may have a curved surface shape that is twisted along the longitudinal direction further than the vertical wall portion having the target shape.

For example, the angle formed by the top plate equivalent part and the vertical wall portion at the center of the convex curve of the intermediate molded product is defined as the angle between the top plate part and the vertical wall part at the center of the convex curve of the target shape, and the length of the intermediate molded product is The angle formed by the top plate equivalent portion and the twisted vertical wall portion at the end portion in the direction may be made larger than the angle formed by the top plate portion and the vertical wall portion at the longitudinal end portion of the target shape.

<About the press method>
Even if the twisted vertical wall portion 25a is formed in the first forming step to cause in-plane shear deformation as described above, wrinkles may be generated in the flange corresponding portion 27 due to compressive deformation. .. In such a case, the first molding step is preferably draw molding in which the blank holder 215 and the die 211 clamp the end of the blank 201 while press-molding, as shown in FIGS. 15(a) and 15(b).
On the other hand, in the second molding step, the intermediate molded product 203 is bent at the punch shoulder R portion 24 between the top plate corresponding portion 23 and the vertical wall corresponding portion 25, and the twisted vertical wall portion of the intermediate molded product 203 is formed into the target shape. Is molded on the vertical wall of the. Therefore, the second molding step may be a foam molding in which the intermediate molded product 203 is sandwiched between the die 221 and the punch 223 and press-molded as shown in FIGS. 15(c) and 15(d). However, if wrinkles are likely to occur in the flange portion of the press-formed product 205 that is press-formed in the second forming step, draw forming may be applied in the second forming step.

In the draw molding and the foam molding, the punch 213 (FIGS. 15(a) and 15(b)) or the punch 223 (FIGS. 15(c) and 15(d)) is paired with a pad (not shown) on the die 211 (FIG. 15). 15(a), (b)) side or the die 221 (FIGS. 15(c), (d)) side, and using the pad, in the first molding step, the top plate equivalent portion 203a of the intermediate molded product 203. The portion 201a (see FIG. 15(a)) of the blank 201 corresponding to (1) may be molded by pressing the top plate equivalent portion 203a (see FIG. 15(c)) of the intermediate molded product 203 in the second molding step.

A specific press-molding experiment was conducted on the effect of the press-molding method according to the present invention, which will be described below.

In the press molding experiment, as shown in FIG. 2, a cross-sectional hat shape having a top plate portion 3, a vertical wall portion 5, and a flange portion was obtained, and the top plate portion 3 and the flange portion 7 were along the longitudinal direction in a side view. A press-formed product 1 having a convex curved portion 11 curved in a convex shape in the height direction and linear portions 13 extending on both sides in the longitudinal direction was used as a molding target.

As shown in FIG. 16, the dimensions of the press-formed product 1 are as follows: the width of the top plate portion 3 is 60 mm, the height of the vertical wall portion 5 is 70 mm, the width of the flange portion 7 is 20 mm, and the top plate portion 3 and the vertical wall are The angle formed by the part 5 was set to 80°. Furthermore, the length in the longitudinal direction is 385 mm, the radius of curvature of the curve of the convex curved portion 11 is R150 mm, and the angle between the top plate portion 3 and the press molding direction in the straight line corresponding portion 33 when viewed from the side is an acute angle side angle. θ ₀ was set to 70°.
The material used for press forming in the experiment was a steel plate having a plate thickness of 1.2 mm and a tensile strength of 1180 MPa.

Here, the pressing method in the first molding step is draw molding (see FIGS. 15A and 15B), and the pressing method in the second molding step is foam molding (see FIGS. 15C and 15D). ). Here, in the first step, the blank holder load was set to 20 tonf.

In the first molding step, as shown in FIG. 6, a top plate corresponding portion 23, a vertical wall corresponding portion 25 including a twisted vertical wall portion 25a having a shape twisted along the longitudinal direction, and a flange corresponding portion 27 are formed. Then, the intermediate molded product 21 having the portion 31 corresponding to the convex curve is press-molded. Here, the twisted vertical wall portion 25a has a longitudinal length L of 250 mm and a vertical wall height H of 70 mm (see FIG. 8).

FIG. 17 shows the cross-sectional shape of the intermediate molded product 21. In the present embodiment, compared with the angle θ ₁ formed by the top plate equivalent portion 23 and the twisted vertical wall portion 25a at the longitudinal center (FIG. 17A) of the convex curved equivalent portion 31, the twisted vertical wall portion 25a An example of the present invention is one in which the angle θ ₂ formed with the top plate equivalent portion 23 at the end portion in the longitudinal direction (FIG. 17B) is larger. Then, the angle difference Δθ (=θ ₂ −θ ₁ ) is variously changed by changing the _two angles θ ₁ and θ ₂ , and the intermediate molded product 21 is press-molded in the first molding process, and then the second The press formability was evaluated by the presence or absence of cracks and wrinkles in the press-formed product 1 press-formed into the target shape in the forming process.

Regarding the evaluation of cracks, "X" was given when there was a crack, "△" was given when there was no crack but there was a constriction due to the reduction in sheet thickness, and "○" was given when there was no crack or constriction.
Regarding the evaluation of wrinkles, "x" was given when there were noticeable wrinkles, "△" when there were minute wrinkles, and "○" when there were no wrinkles.

In this embodiment, the press-formed product 1 is press-formed in one step of foam molding or draw molding, and the press-formed product 1 is press-formed in two steps of the first molding step and the second molding step. In the conventional example, the vertical wall equivalent portion 25 of the intermediate molded product 21 press-molded in the first molding step is not a curved surface shape twisted along the longitudinal direction.

Further, the press-molded product 1 is press-molded in two steps of a first molding process and a second molding process, and the top plate equivalent part 23 of the intermediate molded product 21 press-molded in the first molding process and the twist vertical A comparative example was one in which the angles θ ₁ and θ ₂ formed with the wall portion 25a were out of the range of the present invention.

Then, with respect to the press-formed products according to the conventional example and the comparative example, the presence or absence of cracks and wrinkles was evaluated as in the case of the present invention.
Table 1 shows the press molding conditions and the evaluation results of the press moldability.

In Table 1, the convex curve central angle θ ₁ is the angle formed by the top plate equivalent portion 23 and the twisted vertical wall portion 25a at the center in the longitudinal direction of the convex curved equivalent portion 31 of the intermediate molded product 21 (FIG. 17). (A)), the longitudinal end angle θ ₂ is an angle formed by the top plate equivalent portion 23 and the twisted vertical wall portion 25a (or the vertical wall equivalent portion 25) at the longitudinal end portion of the twisted vertical wall portion 25a. Yes (Fig. 17(b)). Further, the angle difference Δθ, the length L in the longitudinal direction and the height H of the vertical wall are given in the same manner as in the above-described embodiment, and the twist amount T is the angle difference Δθ, the length L in the longitudinal direction and the vertical wall. It is obtained by substituting the height H into the above equation (1).

In Table 1, Conventional Example 3 to Conventional Example 5, Comparative Example 2 to Comparative Example 4, and Inventive Example 1 to Inventive Example 13 are collectively shown for each condition in which the angle difference Δθ is the same. Further, in Conventional Example 1, the press-formed product 1 is molded in one step of foam molding. Further, in Conventional Example 2, the press-formed product 1 is formed in one step of draw forming, and the angle formed by the top plate portion 3 and the vertical wall portion 5 is 100° which is the target shape.

In Conventional Example 1, the top plate portion 3 was not cracked, but the flange portion 7 was wrinkled.
In Conventional Example 2, wrinkles were not observed in the flange portion 7, but cracks were generated in the top plate portion 3.

In Conventional Example 3 to Conventional Example 5, since the angle difference Δθ between the convex curved central angle θ ₁ and the longitudinal end angle θ ₂ is 0, in-plane shear deformation is applied to the vertical wall equivalent portion 25 to perform intermediate forming. Item 21 could not be press molded. Therefore, in the press-formed product 1 in which the intermediate formed product 21 is press-formed into the target shape, a line length difference in the longitudinal direction between the top plate portion 3 and the flange portion 7 occurs, and cracks in the top plate portion 3 and wrinkles in the flange portion 7 occur. Both could not be suppressed at the same time.

In Comparative Examples 1 to 4, the longitudinal end angle θ ₂ is smaller than the convex curved central angle θ ₁ and the angular difference Δθ is negative. Therefore, in the first forming step, the angle difference Δθ between the convex curved central angle θ ₁ and the longitudinal end angle θ ₂ is not 0, and the twisted vertical wall portion 25a is formed by in-plane shear deformation. Since the direction of the in-plane shear deformation is opposite to the direction of the shear deformation in the twisted vertical wall portion according to the example of the present invention (see FIG. 12 ), the line in the longitudinal direction of the top plate equivalent portion 23 and the flange equivalent portion 27. The length difference did not decrease. As a result, in the press-formed product 1 having the target shape, it was not possible to simultaneously suppress both cracks in the top plate portion 3 and wrinkles in the flange portion 7.

In the present invention examples 1 to 13, the longitudinal end angle θ ₂ is larger than the convex curved central angle θ ₁ and the angular difference Δθ is positive, and the convex curved central angle θ _{1 is} long. The direction end angle θ ₂ , the longitudinal length L of the twisted vertical wall portion 25a and the vertical wall height H are changed.

From Table 1, the invention examples 1 to 4 (Δθ=20°), the invention examples 5 to 7 (Δθ=40°), the invention examples 8 to 9 (Δθ=60°) ), the present invention example 10 (Δθ=80°) and the present invention example 11 (where the convex curved central angle θ ₁ is smaller than the angle (=100°) formed by the top plate portion 3 and the vertical wall portion 5 of the target shape ( θ ₁ =95°), the longitudinal length L of the twisted vertical wall portion 25a and the vertical wall height H are both changed in the present invention example 12 (L=125 mm) and the present invention example 13 (H=35 mm). It was shown that a press-formed product can be press-formed by suppressing both cracks and wrinkles at the same time.

This is because in the intermediate molded product 21 according to Inventive Example 1 to Inventive Example 13, the twisted vertical wall portion 25a is subjected to in-plane shear deformation as shown in FIG. It is considered that this is because the occurrence of a line length difference in the longitudinal direction between the portion 3 and the flange portion 7 is reduced.
Furthermore, the present invention example 5 to the present invention example 7 (T=11.2°), the present invention example 8 to the present invention example 9 (T=) in which the twist amount T is within the preferred range of the present invention (10° to 20°). 16.8°) and Inventive Example 11 (T=12.6°), no cracks or wrinkles were found in the press-formed product 1 and good results were obtained.

As described above, according to the press-molding method of the present invention, a press-molded product having a hat-shaped cross-section that is convexly curved in the height direction along the longitudinal direction in a side view is formed by suppressing both cracks and wrinkles. It has been demonstrated that it can be done.

1 Press-formed product 3 Top plate part 4 Punch shoulder R part 5 Vertical wall part 6 Die shoulder R part 7 Flange part 11 Convex curved part 13 Straight part 21 Intermediate molded product 23 Top plate equivalent part 24 Punch shoulder R part 25 Vertical wall Corresponding part 25a Twisted vertical wall part 26 Die shoulder R part 27 Flange equivalent part 31 Convex curved equivalent part 33 Straight equivalent part 41 Intermediate molded product 43 Top plate equivalent part 45 Vertical wall equivalent part 45a Twisted vertical wall part 47 Flange part 51 Convex Curved equivalent part 53 straight equivalent part 61 intermediate molded product 63 top plate equivalent part 65 vertical wall equivalent part 65a twisted vertical wall part 67 flange part 71 convex curved equivalent part 73 straight line equivalent part 81 intermediate molded product 83 top plate equivalent part 85 Vertical wall equivalent part 85a Twisted vertical wall part 87 Flange part 91 Convex curved equivalent part 93 Straight line equivalent part 101 Intermediate molded product 103 Top plate equivalent part 105 Vertical wall equivalent part 105a Twisted vertical wall part 107 Flange equivalent part 111 Convex curved equivalent part Part 113 Straight part 121 Press-formed product 123 Top plate part 125 Vertical wall part 127 Flange part 131 Convex curved part 133 Straight part 141 Press-formed product 143 Top plate part 145 Vertical wall part 147 Flange part 151 Convex curved part 153 Straight line Part 201 Blank 201a Part 203 Intermediate molded product 203a Top plate equivalent part 205 Press molded product 211 Die 213 Punch 215 Blank holder 221 Die 223 Punch

Claims (2)

A top plate part, a vertical wall part continuous from the top plate part, and a cross-sectional hat shape having a flange part continuous from the vertical wall part, wherein the top plate part and/or the flange part is long in a side view. A press-molding method for molding a press-molded article having a convex curved portion that is curved convexly in a height direction along a direction,
A top plate corresponding part corresponding to the top plate part and a vertical wall corresponding part corresponding to the vertical wall part and including a twisted vertical wall part having a twisted shape along the longitudinal direction are formed, and the convex curve A first molding step of press molding an intermediate molded product having a portion corresponding to a convex curve corresponding to the portion;
A second molding step of press-molding the intermediate molded product into the press-molded product,
The twisted vertical wall portion in the first molding step is twisted such that an angle formed with the top plate equivalent portion is larger on the end side than at the center in the longitudinal direction of the convex curved equivalent portion. Press forming method. The press forming method according to claim 1, wherein the twist vertical wall portion in the first forming step is set so that the twist amount T given by the following equation is in a range of 10° or more and 20° or less. ..
T=Δθ×(H/L)
However,
Δθ: Angle difference (=θ ₂ −θ ₁ )
θ ₁ : Angle (°) between the vertical wall of the twist and the equivalent part of the top plate at the center in the longitudinal direction of the part corresponding to the convex curve
θ ₂ : Angle (°) between the vertical wall of the twist and the top plate equivalent at the longitudinal end of the vertical wall
H: Vertical wall height of twisted vertical wall (mm)
L: Length of twisted vertical wall in the longitudinal direction (mm)